Data Representation and Safety – SS1 Digital Technologies Lesson Note (First Term)

The Smallest Pieces (Bits and Bytes)

Computers are made of millions of tiny switches. These switches can only be in two states: ON or OFF. Because of this, everything in a computer is built out of just two numbers: 0 and 1.

• BIT: This is the smallest unit of information. The word comes from Binary digIT. One bit is just a single 0 or 1.
• BYTE: One bit is too small to do much, so we group them together. 8 Bits make 1 Byte.

Why is a Byte important? One Byte (8 bits) is exactly what a computer needs to store one single character, like the letter “A” or the number “7.”

The Size Scale:

• Kilobyte (KB): About 1,000 bytes (A short paragraph of text).
• Megabyte (MB): About 1 million bytes (A high-quality photo).
• Gigabyte (GB): About 1 billion bytes (A movie).
• Terabyte (TB): About 1 trillion bytes (A whole library of books).

Representing Text (ASCII and Unicode)

If you type the letter “B” on your keyboard, the computer doesn’t actually see a “B.” It sees a code. We use standard “dictionaries” to make sure every computer agrees on which number represents which letter.

1. ASCII (pronounced ASK-ee)

In the early days, we used ASCII. It uses 7 or 8 bits to represent characters.

• The Problem: It only had enough room for 128 or 256 characters. This was fine for English, but it didn’t have room for symbols, emojis, or languages like Arabic, Chinese, or Yoruba.

2. Unicode

Unicode is the modern standard. It uses more bits (usually 16 or 32), which gives it enough room for over 140,000 characters.

• The Result: Because of Unicode, you can send an emoji ✌️ or type in any language in the world, and the computer will understand it.

Representing Images (Pixels and Dots)

How does a computer turn 1s and 0s into a beautiful photo of a sunset? It breaks the image down into a grid of tiny dots called Pixels (Picture Elements).

• Resolution: This is the number of pixels on the screen. More pixels mean a clearer, sharper image.
• Color Depth: Each pixel is assigned a binary code that tells it what color to be.
  1. If we use 1 bit per pixel, the image can only be Black or White.
  2. If we use 24 bits per pixel, we can show over 16 million different colors!

Representing Sound (Sampling)

Sound travels in waves. But computers can’t store a “wave”—they can only store numbers. To capture sound, the computer takes “snapshots” of the sound wave thousands of times per second. This is called Sampling.

• Sample Rate: This is how often the computer takes a snapshot. The more snapshots (samples) it takes per second, the more the digital music sounds like the real thing.
• Standard Quality: For a CD-quality song, the computer takes 44,100 samples every single second!

Summary and Comparison

To wrap up, remember that the computer is like a giant translator.

1. Text becomes numbers through ASCII or Unicode.
2. Pictures become numbers by measuring the color of Pixels.
3. Sound becomes numbers by taking Samples of a wave.

Why should we care? When you understand data representation, you understand why a high-quality video takes up more space (more pixels and more samples) than a text message. It helps you manage your phone storage and understand why some files are “too big” to send.

Class Work / Review

1. How many bits are in 3 bytes?
2. What is the main difference between ASCII and Unicode?
3. If an image is “pixelated” (blurry and blocky), what does that tell you about its pixels?
4. Why does a 5-minute song take up more storage space than a 5-page Word document?